UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  2,  No.  5,  pp.  191-204,  plates  36-28  October  19,  1920 


INTERSPECIFIC  HYBRIDS  IN  CREPIS 

I.  CREPIS  CAPILLARIS  (L.)  WALLR.  X  C.  TECTORUM  L. 

BY 

ERNEST  B.  BABCOCK  and  JULIUS  L.   COLLINS 


Although  the  problem  of  the  mechanism  of  heredity  may  be  said 
to  have  been  solved  by  Morgan  and  others1  by  means  of  the  genetic 
analysis  of  a  species  of  flies,  Drosopltila  melanogaster,  there  yet 
remains  the  highly  important  question  regarding  the  generality  of 
the  conclusions  based  on  the  Drosophila  data.  As  has  been  pointed 
out  by  Morgan,2  no  method  of  determining  the  specific  relation  of 
individual  chromosomes  to  particular  somatic  characters  appears  more 
promising  than  the  study  of  hybrids  between  species.-  Especially  is 
this  the  case  when  the  species  possess  low  chromosome  numbers.  If 
such  species  can  be  subjected  to  extensive  genetic  analysis  so  that  the 
factorial  composition  of  each  pair  of  chromosomes  may  be  described 
with  some  degree  of  exactness,  and  if  fertile  hybrids  between  such 
species  can  be  obtained  so  as  to  permit  of  breeding  as  well  as  of  cyto- 
logical  investigations  of  the  hybrid  progeny,  we  should  find  here  the 
most  promising  material  with  which  to  test  the  generality  of  the 
chromosome  theory  of  heredity. 

Inasmuch  as  several  species  of  Crepis  were  known  to  possess  low 
chromosome  numbers,  considerable  attention  has  been  given  by  the 
writers3  to  the  genetic  investigation  of  two  of  these  species,  viz., 
Crepis  capillaris   (vircns)'1  and  C.  tectorum  L.,  the  results  of  which 


i  Morgan,  T.  H.,  Sturtevant,  A.  II.,  Muller,  H.  J.,  and  Bridges,  C.  B.,  The 
Mechanism  of  Mendelian  Heredity.  New  York,  Holt,  xiii  +  262  pp.,  frontispiece, 
and  unnumbered  diagrams.     1915. 

2  Morgan,  T.  H.,  The  Physical  Basis  of  Heredity.  Philadelphia,  Lippincott, 
pp.  1-305,  117  illustrations.     1919. 

3  Babcock,  E.  B.,  "Crepis — a  promising  genus  for  genetic  investigations." 
Amer.  Nat.,  vol.  54  (1920),  pp.  270-276. 

*  Britten,  James,  and  Rendle,  A.  B.,  "Notes  on  the  'List  of  British  Seed 
Plants.'  "    Jour.  Bot.,  vol.  45  (1907),  p.  102. 


192  University  of  California  Publications  in  Agricultural  Sciences        [Vol.  2 

will  be  reported  later.  But  before  confining  our  attention  too  largely 
to  one  or  two  species  only,  it  was  deemed  advisable  to  look  into  the 
possibility  of  obtaining  fertile  hybrids  between  these  species. 

Although  the  species  in  question  show  differences  in  many  morpho- 
logical characters  and  in  at  least  one  physiological  character,  only 
those  having  to  do  with  the  seedling  stage  will  be  considered  here, 
due  to  the  fact  that  the  hybrids  in  all  cases  died  during  this  stage. 

The  achenes  of  Crepis  capillaris  range  in  length  between  2.0  and 
2.5  mm. ;  they  have  no  beak,  and  the  pappus  sheds  rather  easily.  The 
cotyledons  vary  from  broadly  ovate  to  the  condition  where  the  breadth 
of  the  widest  part  is  greater  than  the  length,  in  which  case  the  tip  of 
the  cotyledon  is  distinctly  dentate.  The  first  plumule  leaf  makes  its 
appearance  very  quickly  after  the  cotyledons  have  expanded  to  their 
normal  size.  The  cotyledons  are  approximately  5  mm.  wide  and 
4  to  6  mm.  long  (pi.  36,  fig.  2). 

The  achenes  of  Crepis  tectorum  range  from  3.5  to  4  mm.  in  length 
and  are  correspondingly  thicker  than  the  capillaris  achenes.  The 
tectorum  achenes  are  also  beakless  but  they  retain  their  pappus  more 
persistently  than  do  those  of  the  other  species.  The  cotyledons  are 
distinctly  different  in  both  shape  and  size.  The  general  shape  is  nar- 
rowly linear  with  bluntly  pointed  ends.  Length  of  cotyledons  varies 
around  6  mm.,  the  width  around  3  mm.  As  in  capillaris,  the  plumule 
leaves  appear  very  promptly,  usually  one  at  a  time,  but  occasionally 
in  both  species  two  plumule  leaves  appear  simultaneously.  Thus  there 
is  evident  a  distinct  difference  in  size  and  shape  of  the  first  or  cotyledon 
leaves  of  the  two  species  corresponding  with  the  difference  in  size  of 
achenes,  and  a  resemblance  in  the  prompt  appearance  of  the  plumule 
leaves  (pi.  36,  fig.  1). 

Crepis  tectorum  possesses  one  more  pair  of  chromosomes  than  C. 
capillaris,  the  former  having  four  pairs,  the  latter,  three  pairs  (pi.  38, 
fig.  2). 

Two  methods  of  pollination  were  employed,  which  will  be  described 
in  detail  in  another  paper:  (1)  Emasculation  of  female  parent  flowers; 
(2)  female  parent  not  emasculated  but  washed  free  of  its  own  pollen 
by  use  of  a  fine  jet  of  water.  The  second  method  was  used  when  the 
capillaris  plant  had  given  indications  from  selfing  tests  of  being  self- 
sterile.  The  results  of  cultures  thus  secured  are  indicated  below.  The 
female  parent  is  mentioned  first  in  each  cross. 


nii'o] 


Babcoclc-Collins :   Crepis  capillaris  X  C.  tectorum 


193 


Culture 

Num- 
ber 

Parents 

Cotyledon 

Characters  of 

Seedlings 

Method  of 
Pollin- 
ation 

Behavior 

of 
Hybrids 

Number 

of 
Seedlings 

Z    3 

capillaris  X  tectorum 

6  tectorum 
5  capillaris 
1  intermediate 

2 

All  failed  to 
pass  cotyledon 
stage 

12 

Z    5 

capillaris  X  tectorum 

All  tectorum, 
showed  hybrid 
vigor 

2 

All  failed  to 
pass  cotyledon 
stage 

6 

Z    7 

capillarisy.tectorum 

All  tectorum, 
showed  hybrid 
vigor 

2 

All  failed  to 
pass  cotyledon 
stage 

3 

Z    8 

capillaris  X  tectorum 

Intermediate 

2 

All  failed  to 
pass  cotyledon 

stage 

1 

Z10 

tectorum  X  capillaris 

All  tectorum, 
showed  hybrid 
vigor 

1 

All  failed  to 
pass  cotyledon 
stage 

12 

Z  12 

capillaris  X  tectorum 

Small  and  dis- 
torted, abnormal 

1 

Failed  to  pass 

cotyledon 

stage 

1 

Z13 

capillaris  X  tectorum 

Small  and  dis- 
torted, abnormal 

2 

All  failed  to 
pass  cotyledon 
stage 

5 

Z  3  Fx  (18.42  P21  X  p2  P51)  capillaris  X  tectorum 

Three  heads  from  which  pollen  had  been  washed  with  a  jet  of  water 
were  then  pollinated  with  tectorum  pollen  and  covered  with  a  bag. 
These  heads  produced  forty-two  achenes  which  were  smaller  even  than 
the  average  capillaris  achenes.  Of  twenty-four  placed  in  the  germi- 
nator,  thirteen  sprouted  and  the  twelve  surviving  divided  themselves 
in  the  cotyledon  stage  into  three  groups.  Six  appeared  like  tectorum 
seedlings,  five  like  capillaris,  and  one  was  intermediate.  These  all  died 
at  the  end  of  the  cotyledon  stage. 


Z5Fj  (18.58  P4  X  p2  P10)  capillaris  X  tectorum 

Achenes  from  this  cross  were  planted  at  two  different  times.  Of 
the  four  placed  first  in  the  germinator,  only  two  sprouted,  both  having 
large  tectorum-like  cotyledons.     The  plumule  leaves  started  on  one 


194  University  of  California  Publications  in  Agricultural  Sciences        [Vol.  2 

plant  but  failed  to  appear  on  the  other.  After  remaining  alive,  but 
not  growing,  for  eighty-one  days  the  plant  with  the  rudimentary 
plumule  died.  The  one  failing  to  produce  even  the  rudimentary 
plumule  leaves  lived  for  a  shorter  period. 

After  this  unsuccessful  attempt,  twelve  remaining  achenes  were 
placed  in  the  germinator.  At  the  end  of  five  days  five  had  sprouted, 
four  of  which  showed  robust,  healthy  cotyledons  which  resembled  those 
of  tectorum  seedlings  but  on  an  enlarged  scale.  They  were  essentially 
as  the  first  two  plants  secured  from  the  same  lot  of  seed.  After  having 
produced  abnormally  large  cotyledon  leaves,  and  in  some  cases  rudi- 
ments of  plumule  leaves,  all  the  seedlings  began  to  turn  yellowish,  and, 
despite  efforts  to  revive  or  stimulate  them,  continued  to  decline  until 
finally  they  died. 

One  of  the  plants  which  was  beginning  to  show  signs  of  distress 
was  carefully  removed  from  the  soil  by  washing  in  a  pan  of  water. 
The  root  was  one  inch  long  and  had  a  blunt  rounded  tip  covered  by 
the  rootcap.  All  along  the  root  from  the  tip  to  the  ground  surface 
line  were  small  knots  or  wartlike  protuberances  as  if  lateral  roots 
might  have  been  attempting  to  push  out.  Later  cytological  examina- 
tion showed  this  to  be  the  case.  The  root  and  the  cap  were  turning 
brownish  as  if  growth  had  ceased  and  decomposition  had  begun, 
although  the  above-ground  parts  had  only  begun  to  show  signs  of 
unhealthiness.  The  fifth  plant  of  this  culture  was  smaller  than  the 
others  but  otherwise  like  them. 

When  the  plants  began  to  show  symptoms  of  declining  health  some 
of  them  were  treated  with  ether  in  an  effort  to  stimulate  them  to  new 
growth,  but  this  appeared  to  have  no  effect  and  all  perished. 

%  7  Pj  (18.204  PB  X  p2  P51)  capillaris  X  tectorum 

Eight  Fx  achenes  were  produced.  Three  out  of  five  achenes  pro- 
duced seedlings  which  showed  their  hybrid  nature  by  developing  large 
tectorum-like  cotyledons,  by  their  failure  to  produce  plumule  leaves, 
and  by  their  inability  to  pass  beyond  the  cotyledon  stage. 

Z8F;    (18.201  Px   X   p2  P51)    CAPILLARIS   X   TECTORUM 

Only  one  achene  was  produced  on  one  head  washed  free  of  its  own 
pollen  and  pollinated  with  tectorum  pollen.  This  achene  produced  a 
seedling  which  appeared  to  be  intermediate  between  its  parents,  and 
like  other  hybrid  seedlings  died  at  the  end  of  the  cotyledon  stage. 


1920]  Babcock-Collins :   Crepis  capillaris  X  C.  tectorum  195 

Z  10  Ft  (p2  P51  X  e4  P2)  tectorum  X  capillaris 

This  represents  the  reciprocal  of  the  above  mentioned  crosses  in 
which  capillaris  was  used  as  the  female  parent.  All  tectorum  flowers 
used  in  hybridization  work  were  emasculated  in  the  bud  stage. 

Six  Pj  seedlings  were  secured,  all  exhibiting  tectorum  cotyledons 
on  an  enlarged  scale.  All  died  at  the  end  of  the  cotyledon  stage,  some 
having  started  to  produce  plumule  leaves  which  resulted  only  in 
rudimentary  and  abnormally  shaped  structures  too  small  to  be 
described  in  detail.  Ether  treatment  of  two  slowly  dying  seedlings 
failed  to  stimulate  them  to  renewed  growth.  These  plants  remained 
alive  in  the  cotyledon  stage  thirty  days. 


Z  12  Ft  (18.42  Px  X  p2  PB1)  capillaris  X  tectorum 

In  this  culture  capillaris  flowers  were  emasculated  in  the  bud  stage 
before  the  stigma  was  receptive.  Three  heads  produced  four  achenes, 
only  one  of  which  sprouted.  It  produced  a  small  plant  with  under- 
sized distorted  cotyledons  and  no  plumule.  This  weak  seedling  died 
in  the  cotyledon  stage. 


Z  13  F1  (el4  P.  X  212  P21)  capillaris  X  tectorum  (Kew) 

One  washed  head  produced  eight  achenes.  Three  sprouted,  and  the 
plants  had  enlarged  cotyledons  which  persisted  for  some  time.  One 
seedling  produced  several  abortive  plumule  leaves  but  they  all  stopped 
growing  when  about  4  or  5  mm.  long.  It  appeared  unable  to  produce 
typical  plumule  leaves.  Those  formed  were  tiny  threadlike  structures 
and  not  at  all  like  plumule  leaves  of  normal  seedlings.  The  diameter 
of  this  plant  at  sixty  days  was  three  fourths  of  an  inch.  (Some  of  the 
normal  tectorum  plants  produce  seed  in  ninety  days.)  Another  seedling 
went  through  essentially  the  same  process  and  died  when  four  months 
old.  The  third  plant  had  twisted,  deformed  cotyledons,  and  each 
appeared  to  have  a  separate  root.  They  were  separated,  each  cotyledon 
placed  in  a  pot  of  soil,  where  one  died  after  four  days,  the  other  con- 
tinuing the  struggle  for  thirty-six  days  before  it  too  perished. 

It  will  be  noted  that  cultures  Z  10  and  Z  12  are  reciprocal  crosses 
in  which  each  female  parent  was  emasculated,  thus  insuring  hybridity, 
and  that  the  behavior  of  the  resulting  seedlings  was  similar.  The 
plants  of  both  cultures  failed  to  develop  past  the  stage  in  which  the 


196  University  of  California  Publications  in  Agricultural  Sciences        [Vol.  2 

young  seedling  is  nourished  from  the  food  material  stored  in  the  seed. 
Apparently  in  the  combination  of  capillaris  and  tectorum  the  germinal 
elements  are  incapable  of  interacting  in  such  a  way  as  to  cause  the 
seedling  to  develop  normally  (pi.  36,  fig.  3). 

In  a  number  of  cases  (not  listed)  where  the  capillaris  female  parent 
was  washed  and  pollinated  with  tectorum  pollen,  a  number  of  achenes 
were  secured  which  germinated  well,  producing  seedlings  which 
appeared  and  behaved  in  every  way  like  typical  capillaris  plants. 
These  did  not  stop  growth  at  the  end  of  the  cotyledon  stage  but  con- 
tinued normal  development.  They  were  maternal  in  all  respects.  Thus 
we  get  two  kinds  of  results  when  depollination  by  water  is  substi- 
tuted for  emasculation,  and  tectorum  pollen  applied:  (1)  plants  which 
show  the  tectorum  type  of  cotyledon  on  an  enlarged  scale,  and  which 
die  at  the  end  of  the  cotyledon  stage  of  development ;  (2)  plants  which 
show  maternal  inheritance  and  are  able  to  develop  past  the  cotyledon 
stage,  the  limit  of  development  in  class  one.  Class  two  occurs  only 
when  capillaris  is  the  female  parent  and  the  water  method  of  depollina- 
tion is  used.  Of  eleven  crosses  where  the  female  was  depollinated  by 
means  of  the  water  jet,  six  produced  F1  seedlings  having  tectorum 
cotyledons  on  an  enlarged  scale,  and  all  six  failed  to  develop  beyond 
the  cotyledon  stage ;  five  produced  Fx  seedlings  typically  capillaris 
which  developed  normally  into  capillaris  plants. 

From  the  evidence  furnished  by  the  equivalent  results  of  reciprocal 
crosses  when  the  female  plant  was  emasculated  (Z  10  and  Z  12),  we  are 
led  to  conclude  that  seedlings  of  the  second  class  described  above, 
exhibiting  maternal  inheritance,  were  the  result  of  self-fertilization 
of  the  capillaris  plant,  which  may  have  occurred  before  washing  or 
because  of  incomplete  removal  of  the  pollen  by  the  water  method,  and 
that  those  of  the  first  class,  showing  dominance  of  tectorum  in  F1  and 
the  failure  to  continue  development,  were  true  hybrids.  As  a  check 
a  number  of  heads  were  depollinated  with  water  and  bagged  without 
pollination.  In  one  case  selfed  seeds  were  produced  in  a  bag  covering 
heads  so  treated.  This  indicates  that  the  method  is  responsible  for 
the  appearance  of  the  capillaris  plants  where  crossing  was  attempted. 
In  no  case  were  achenes  produced  on  heads  which  had  been  emasculated 
and  bagged  without  pollination  as  checks. 

The  above  conclusions  were  confirmed  by  cytological  examination. 
Cells  from  the  mature  plants  (Z  9  P„)  were  found  to  contain  six 
chromosomes,  the  typical  number  for  capillaris.  Cells  of  the  root  tips 
from  young  seedlings  of  the  hybrid  class  (Z  5)  were  found  to  contain 


1920]  Babcock-Collins:   Crepis  capillaris  X  C.  tectorum  197 

seven  chromosomes,  the  sum  of  the  haploid  numbers  of  capillaris  and 
of  tectorum.  Nothing  can  be  learned  of  the  reduction  division 
because  the  plants  never  reached  maturity,  but  there  seems  to  be  no 
difficulty  in  somatic  division,  all  seven  of  the  chromosomes  dividing 
in  an  apparently  normal  fashion. 

Examination  of  a  young  ¥t  seedling  (Z  5)  which  had  reached 
the  limit  of  development,  revealed  a  most  unusual  teratological  cell 
condition  (pis.  37  and  38).  The  tissue  systems  of  the  plant  were  in 
a  chaotic  condition.  Patches  of  embryonic  tissue  were  distributed 
here  and  there  among  the  larger  vegetative  cells,  patches  or  sections 
of  tracheary  cells  were  likewise  distributed  here  and  there  throughout 
the  mass.  Groups  of  vegetative  cells  were  separated  by  streaks  of 
disorganized  and  disintegrated  tissue.  It  apeared  as  if  the  force  that 
directs  the  organization  and  coordination  of  cell  systems,  whatever  it 
is,  was  lacking.  This  lack  of  order  in  the  cell  systems  prevented  the 
functioning  of  these  systems  and  caused  cessation  of  development. 

The  principal  features  of  the  interspecific  hybrids  here  recorded 
are : 

1.  Reciprocal  crosses  are  equivalent. 

2.  Fj  shows  dominance  of  tectorum  cotyledon  characters  and  hybrid 
vigor,  as  expressed  by  the  increased  size  of  the  seedling  parts. 

3.  Absence  of  complete  organization  and  coordination  of  the  func- 
tioning systems,  which  absence  causes  the  death  of  the  plant  at  the 
end  of  the  cotyledon  stage. 

The  possible  origin  of  species  having  a  larger  chromosome  number 
from  species  having  a  smaller  number  by  fragmentation  or  segmenta- 
tion of  some  of  the  latter  has  been  suggested  a  number  of  times.  Metz5 
shows  a  diagrammatic  gradation  of  chromosome  numbers  for  different 
species  of  Drosophila.  Hance6  applies  the  same  idea  to  the  origin  of 
chromosome  number  variations  in  Oenothera  species.  Rosenberg7 
recently  concluded  that  the  origin  of  Crepis  species  with  three,  four, 
and  five  pairs  of  chromosomes  could  best  be  explained  by  non-dis- 
junction occurring  during  the  reduction  division.     Bridges8  actually 


5  Metz,  C.  W.,  "Chromosome  Studies  in  the  Diptera,  I.  A  preliminary  study 
of  five  different  types  of  chromosome  groups  in  the  genus  Drosophila."  Jour. 
Exp.  Zool.,  vol.  17  (1914),  pp.  45-59. 

6  Hance,  E.  T.,  "Variations  in  the  number  of  somatic  chromosomes  in 
CEnothera  scintillans  de  Vries. "     Genetics,  vol.  3  (1918),  pp.  225-261. 

7  Kosenberg,  O.,  "Chromosomenzahlen  und  Chromosomendimensionen  in  der 
Gattung,  Crepis."    Arkiv  for  BotaniJc,  Bd.  15  (1918),  p.  11. 

s  Bridges,  C.  B.,  "Non-disjunction  as  proof  of  the  chromosome  theory  of 
heredity."    Genetics,  vol.  1  (1916),  pp.  1-52  and  107-163. 


198  University  of  California  Publications  in  Agricultural  Sciences        [Vol.  2 

found  a  female  Drosophila  melanogaster  with  five  pairs  of  chromosomes 
which  originated  after  secondary  non-disjunction  in  both  parents. 

Assuming  that  Crepis  tectorum,  a  species  with  four  pairs  of 
chromosomes,  originated  by  non-disjunction  of  one  pair  of  the  capil- 
laris chromosomes,  we  would  expect  a  cross  between  these  two  to  be 
compatible  inasmuch  as  the  chromosome  complex  should  be  identical, 
tectorum  merely  having  one  of  the  capillaris  chromosomes  in  duplicate. 

The  demonstrated  inability  of  hybrids  between  the  two  species  to 
function  normally  leads  to  the  conclusion  that  Crepis  tectorum  is  not 
related  in  such  a  direct  way  to  Crepis  capillaris. 

The  results  reported  here  indicate  the  desirability  of  making  pre- 
liminary experiments  in  hybridizing  all  the  species  of  Crepis  that  give 
promise  of  being  of  value  for  genetic  investigations.  Experiments 
with  other  species  are  now  under  way. 

Grateful  acknowledgment  is  made  to  Dr.  Ruth  F.  Allen  for  her 
assistance  in  preparing  the  cytological  material. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://archive.org/details/interspecifichyb25babc 


EXPLANATION  OF  PLATES 

PLATE  36 
Crepis  seedlings.     X  2. 

Fig.  1.  Crepis  tectorum.  Normal  seedling  showing  elongated  cotyledons 
extending  horizontally  from  the  center.  Note  the  two  plumule  leaves  at  right 
angles  to  the  cotyledons. 

Fig.  2.  Crepis  capillaris.  Normal  seedling  showing  short  rounded  cotyledons 
extending  horizontally,  one  plumule  leaf  showing  at  right  angles  to  the 
cotyledons. 

Fig.  3.  F,  hybrids,  C.  tectorum  $  X  C.  capillaris  <$  (above).  Ft  hybrids,  C. 
capillaris  $  X  C.  tectorum  $  (below).  Seedlings  show  stage  at  which  develop- 
ment ceases. 

Fig.  4.  Selfed  seedling  resulting  from  crossing  method  No.  2.  Note  the 
roundish  C.  capillaris  type  of  cotyledons  (marked  c)  not  at  all  like  those  of  the 
Fj  hybrids.  Five  plumule  leaves  are  shown,  the  plant  being  the  same  age  as 
the  hybrids. 

Fig.  5.  Fj  hybrid  seedling  produced  by  crossing  method  No.  2.  Notice  the 
two  small  abnormal  plumule  leaves  between  the  cotyledons.  This  shows  the 
highest  stage  to  which  any  of  the  hybrids  developed. 


[200] 


UNIV. 


CALIF.    PUBL.    AGR.    SCI.    VOL.    2  |  BABCOCK-COLLINS]    PLATE    36 


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PLATE  37 

Teratologieal  tissue  of  F,  hybrid  Crcpis  capillaris  X  C.  tcctorum.    Z  5. 

Fig.  1.  A  vertical,  not  quite  median,  longitudinal  section  of  the  abortive 
plumule  of  a  seedling.     X  530. 

a.  An  isolated  patch  of  tissue  surrounded  by  the  slime  (dark  in  reproduc- 
tion) of  disintegrating  cells.  Within  the  patch  are  the  leaf  tracheids  and  an 
irregular  mass  of  meristematic  dividing  cells. 

b.  Above  the  main  patch  of  meristem  is  a  second  smaller  layer,  also  lying 
free  in  a  layer  of  slime.  It  is  about  ten  cells  long  and  two  or  three  cells  thick. 
The  cells  nearest  it  on  all  sides  are  fully  matured  parenchyma. 

c.  Side  section  of  apex  of  plumule  showing  only  mature  cells. 


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UNIV.    CALIF.    PUBL.    AGR.    SCI.    VOL.    2  [BABCOCK-COLLI NS  J    PLATE    37 


PLATE  38 

Fig.  1.  Teratological  tissue  in  Ft  hybrid  Crepis  capiUaris  X  tectorum.  Z  5. 
Cross-section  of  root  just  below  ground  level.     X  530. 

a.  A  vegetative  cell  dividing  (metaphase).  This  cell  is  completely  sur- 
rounded by  fully  differentiated  cells. 

b.  Very  much  crumpled  and  distorted  cells  of  outer  wall  of  seedling. 

c.  Black  areas  showing  decomposition  of  cells. 

Fig.  2.  Chromosomes  of  Crepis  capiUaris.  Polar  view  showing  two  J  's  and 
four  more  or  less  rodlike.     X  1500. 

Fig.  3.  Chromosomes  of  Fj  hybrid  C.  capiUaris  X  C.  tectorum  (Z  5)  show- 
ing two  J's,  one  V,  and  rodlike  ones.     X  1500. 


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UNIV,    CALIF.    PUBL.    AGR.    SCI.    VOL,    2 


[BABCOCK-COLLINS]    PLATE    38 


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